1. Field of the Invention
The present invention relates to a horizontal/vertical conversion transporting apparatus for transporting a boat which carries semiconductor wafers or the like.
2. Description of the Related Art
Various types of transporting apparatuses which hold articles to transport them to predetermined positions have been used. A typical example is a wafer boat transporting apparatus for holding a wafer boat on which a large number of semiconductor wafers are placed and transported it to a predetermined position. During transfer of an article, i.e., a wafer boat, a small deviation of a transporting position is caused by mechanical backlash in the wafer boat transporting apparatus. The errors of the transporting positions may be accumulated so as to result in a positional error as large as about several mm from the preset position. When an error of the preset position of the wafer boat occurs during transporting, reliability of transfer of the wafer boat is greatly degraded, and it is impossible to provide a highly reliable transporting apparatus.
In order to prevent an error in the preset position of the wafer boat, improvements have been made in a conventional transporting apparatus such that mechanical backlash is minimized and highly precise positioning can be performed. In this case, however, high-precision control causes an increase in cost, and requires complex adjustment of components of the apparatus. In addition, if an error of the preset position of the wafer boat occurs in such an apparatus, the wafer boat and the transporting unit are deformed during transfer of the wafer boat. The position of the boat must then be forcibly corrected.
Stresses may act on the respective parts of the wafer boat, and the wafer boat may be damaged. For example, when a vertically aligned wafer boat is to be transferred, the wafer boat may drop. A holding portion of the transporting apparatus is brought into frictional contact with the wafer boat so as to increase the amount of dust. For this reason, in a fabrication process of semiconductor devices, a countermeasure for reducing an amount of dust must be provided.
It is possible to correct a positional error during the transfer by using, e.g., an image recognition means. In this case, however, the manufacturing cost of the transporting apparatus is greatly increased.